1. Field Of the Invention
The present invention relates to a detecting circuit. More particularly, it relates to a detecting circuit for detecting, for example, an output of a prism-shaped vibrating gyroscope.
2. Description of the Prior Art
FIG. 11 is a circuit diagram showing an example of a conventional detecting circuit which constitutes a background of the present invention. The detecting circuit 1 is used for detecting, for example, an output of a prism-shaped vibrating gyroscope.
Between two piezoelectric elements 3 and the other piezoelectric element 4 of the vibrating gyroscope 2, an exciting signal generating circuit 5 is connected. In this case, the exciting signal generating circuit 5 is connected respectively to the two piezoelectric elements 3 of the vibrating gyroscope 2 via resistances 6. Meanwhile, outputs of these piezoelectric elements 3 are inputted to a differential amplifying circuit 7.
The vibrating gyroscope 2 is subjected to a bending vibration in a direction orthogonal to the main surface of the other piezoelectric element 4 by the exciting signal generating circuit 5. At this time, by adjusting the signals generated by the electrostatic capacity difference between the two piezoelectric elements 3 to be equal to each other, the output from the differential amplifying circuit 7 becomes 0.
If the vibrating gyroscope 2 is rotated about its axis, the Coriolis force is exerted in a direction orthogonal to the vibrating direction of the vibrating gyroscope 2. Accordingly, the vibrating direction of the vibrating gyroscope 2 is shifted from the vibrating direction of the non-rotating state. Thus, an output difference is produced between the two piezoelectric elements 3 and the output is obtained from the differential amplifying circuit 7. The output corresponds to the rotational angular velocity. Accordingly, the rotational angular velocity applied to the vibrating gyroscope 2 can be detected by measuring the output of the differential amplifying circuit.
The electrostatic capacity of the piezoelectric element, however, changes with atmospheric temperature and variations with time, and thus the output from the differential amplifying circuit does not become 0 even during non-rotation and results in a measurement error. In this case, as shown in FIG. 12, besides the signal outputted by the Coriolis force, the signal outputted by the variations in the electrostatic capacity of the piezoelectric element is inputted to the differential amplifying circuit 7. Therefore, a composite signal of these signals is outputted from the differential amplifying circuit 7 and the rotational angular velocity can not be measured accurately.